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Replacing the Battery on the GPS Board

There have been two GPS boards used in the NexStar 8/9.25/11 GPS scopes.  The first was manufactured by Motorola and appeared in the earliest NexStar 8 and 11 GPS models.  More recently, Celestron switched to a board they designed in-house.  Thus, all newer models have the Celestron board.

The CN-16 unit for the "i" series, AS-GT, CGEM, CGE and CGE Pro series uses the Celestron-designed board as found in the newer NexStar GPS scopes.

As described in this article, the battery on this board is rechargeable.  During normal use of the scope, the battery is charged by the 12 volts supplied to the mount.  When the battery loses its charge, the hand control will display the incorrect time until a GPS link is established (normally the GPS module maintains correct time between uses of the scope).  The GPS link will also take longer than normal.  The original board requires at least 40 hours to completely recharge the battery, while the new board requires 24 hours.  Disconnect the hand control (to prevent the scope from tracking while you are away) and power up the scope to charge the battery.

If the battery will no longer hold a charge, it will be necessary to replace it.

Click any of the pictures below for a larger version.


Photo courtesy
Matthias Bopp

The GPS board for the older NexStar GPS telescopes is found inside the base.  Using a 3.5mm or 9/64 inch hex wrench, completely loosen the five screws securing the plastic base cover - the cover with the Aux, Auto Guide, and PC ports. It is not necessary to remove the screws as we will only be lifting the cover, not completely removing it. If you do remove the screws, note that the one in the back is shorter than the rest.

Carefully lift the base cover. Wires run from the cover to the base and only allow the cover to be raised about 2 inches (5cm). Put a rolled-up sock in both gaps between the cover and each fork arm to hold it in place.  The GPS board is on the side opposite the panel with all the connector ports.  The front board shown here is the GPS board.  It is held in place by the two cross-tip screws in the corners.  As you remove these screws and pull the board free, note the connectors on the back side of the board as well as the antenna cable.  Be sure not to drop the screws into the base. 

The battery is held in a clip and is easily replaced.  The battery is a Panasonic ML621 - the one without the solder pins - and is available at http://www.digikey.com for about $2.

When reassembling, be sure the pins on the connectors are well seated and that all cables are routed so that the scope will rotate 360 degrees without snagging anything.

 


Inside the Fork Arm 
Photo courtesy
 Matthias Bopp

 


Outside the Fork Arm
This photo shows the GPS board and the GPS antenna - click for larger version pointing out the antenna.
Photo courtesy
Rick Smith

On newer NexStar GPS telescopes the GPS board is found on the inside of the fork arm with the hand control bracket or on the outside of the fork arm with the hand control bracket - there is no way to tell without removing the plastic covers.  The CN-16 GPS unit also uses this same newer GPS board. 

If you didn't find the board inside the base as described above, try the outside of the fork arm - simply remove the large plastic cover with the hand control holder.  Be sure to unplug the hand control cable first and set the hand control aside.

If you don't find it there, check the inside of the fork arm.  To remove the cover on the inside of the fork arm, you will first need to lift up the base cover.  Use a 3.5mm or 9/64 inch hex wrench and completely loosen the five screws securing the plastic base cover - the cover with the Aux, Auto Guide, and PC ports. It is not necessary to remove the screws as we will only be lifting the cover, not completely removing it. If you do remove the screws, note that the one in the back is shorter than the rest.  Then remove the four screws holding the plastic cover on the inside of the fork arm.  Pull the cover free and set it aside.

The board is held in place by two cross-tip screws.  Make a sketch of the cable connection just to be sure you don't misconnect it later.  Remove the screws (be careful not to drop them into the base) and pull the board free.  Here is the complication - as you will see, the battery is soldered to the board.  At this point, if you are handy with delicate electronics and don't mind the potential risk of destroying the board, you can unsolder and replace the battery.  Otherwise, contact Celestron about sending the board to them for battery replacement.  The battery is a Panasonic ML2020-H1CN and is available at http://www.digikey.com for less than $3.

For the CN-16 GPS unit, open the case and you will see the GPS board mounted within.  Again, it is the same as the board in the late model NexStar 8/9.25/11 GPS telescopes and uses the same ML2020-H1C battery, soldered in place.

 

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